A uniform resource locator (URL) is a reference of a web address for locating an internet resource. In most document formats (such as HTML, excel, doc, and PDF), URLs may be embedded as hyperlinks which point to cited documents stored in local or remote hosts for easy access and reference. Hypertext is text with hyperlinks. In public data repositories and in social media, embedded hyperlinks may reference important information and are often used to implement reference mechanisms, such as tables of contents, footnotes, bibliographies, indexes, letters, and glossaries.